OpenGameArt.org
Sleepwalker's Dream (Peaceful and Thoughtful)
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"Sleepwalker's Dream (Peaceful and Thoughtful)" by axtoncrolley licensed CC-BY-SA 3.0: https://opengameart.org/content/sleepwalkers-dream-peaceful-and-thoughtful
Where to put it: Game credits or video description. If the entry has a "Copyright/Attribution Notice", follow that.